Reservoirs, such as in septic systems, greasetraps, and other effluent disposal systems, accumulate mediums of differing levels and thicknesses such as gases, liquids, solids and semi-solid materials. These types of reservoirs receive incoming waste which settles or separates into discrete levels of different mediums. Typically, there is a medium which floats on top of one of the other mediums. For example, in a septic system there is normally present a scum layer floating on top of the liquid within the reservoir or in a greasetrap there is present a layer of grease and other solid and semi-solid material floating on top of a liquid medium within the reservoir. These reservoirs require periodic maintenance and service based on the levels of the boundaries of the floating medium, the thickness of the floating medium and the levels of the other mediums relative to one another and relative to the dimensions of the reservoir. However, because the reservoirs are buried, access is often difficult, and routine inspections are rare, many years can pass before service is requested or even known to be required. Very often it is not known that service is required until the reservoir has overflowed.
Reservoirs in septic systems receive entering waste water carrying solids. A portion of the solids settle to the bottom of the reservoir and become sludge and a portion of the solids float to the surface to form a layer of scum. Over time, depending on various factors like individual use, reservoir size and site conditions, these solids accumulate and displace a portion of the available reservoir volume creating less settling capacity for the incoming waste liquid and bringing the solid levels closer to the outlet openings of the reservoir. Diminished settling capacity and close proximity of solids to the outlet increase the levels of solids reaching the drainage field which clogs the field and decreases its drainage capacity. Before the solids reach this level, the reservoir should be cleaned. Close proximity of floating solids to the reservoir outlet can also be caused by a change in the liquid level of the reservoir due to either a leak which lowers the scum layer to the bottom outlet opening, or a lowered leaching capacity backing up the system and raising the scum layer to over the top of the outlet. In both cases, the scum layer may actually enter the outlet and clog the drainage field. Thus, detection of rising and lowering liquids over time is helpful in predicting and preventing eventual reservoir or drainage field overflows and waste water backup into nearby buildings.
In addition to the proximity of floating solids to the reservoir outlet and the total solid volume in the reservoir, there are other parameter levels which, when exceeded, indicate that the reservoir should be cleaned. An example of this is the proximity of the sludge level to the outlet. This level could reach a point, regardless of the proximity of floating solids to the outlet, which would necessitate cleaning of the reservoir.
One system, described in U.S. Pat. No. 4,121,094, monitors only the level of the sludge in the reservoir and operates a sludge removal pump when the sludge reaches a predetermined level. Another system, described in U.S. Pat. No. 4,319,998, uses a float located in-line with the outlet pipe from the reservoir to monitor the liquid level rise inside an enclosure caused by the presence of sludge, indicating that the system requires servicing.
However, these systems do not have the capability of monitoring the level and thickness of the scum layer floating on the surface of the waste liquid or other parameters, such as total solid volume and the proximity of sludge to the outlet, and therefore are not capable of providing a complete and accurate assessment of the condition of the reservoir. That is, these prior art systems only monitor one condition, i.e. sludge level, and do not monitor, inter alia, the level and thickness of the scum layer and other important parameters in the reservoir, which, if they reach unacceptable levels indicate that the reservoir should be cleaned.
Another system, described in U.S. Pat. No. 3,025,962, includes two light-sensitive cells, one is used to determine when the bottom layer of scum has reached a certain level and the second light cell is used to determine when the sludge layer has reached a preset height. The light sensitive cells include light sources and light detectors. When either the scum or the sludge layer reaches the respective light-sensitive cells, they interfere with the transmission of light from the sources to the detectors. When this occurs it indicates that either the sludge layer or the scum layer has reached an unacceptable level. That system has a number of shortcomings, however. The detectors of the light-sensitive cells include windows which allows the light emanating from the light sources to pass therethrough. Very often the windows become dirty and cause false readings. In addition, that system does not monitor the liquid level or the top of the scum layer or their distances to the top of the outlet baffle. Moveover, it cannot detect incremental changes in any of the various layered material in the reservoir as it only detects two basic states inside the reservoir and it does not monitor and display changes in the layered material levels relative to one another or relative to the reservoir over time. It also does not store an historical record of the layered material levels. In short, that system is not capable of providing a complete and accurate assessment of the condition of a reservoir.